Electric lamp stem with strain relieving sleeve



ELECTRIC LAMP STEM WITH STRAIN RELIEVING SLEEVE Filed Dec. 18, 1961 A. TIETZE July 7, 1964 2 Sheets-Sheet 1 Fig 1a.

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ELECTRIC LAMP STEM WITH STRAIN RELIEVING SLEEVE Filed Dec. 18, 1961 2 Sheets-Sheet 2 Fgg i2 a lnven tor' AL Fved Ti "L'ze by v His A' t'i'or'neg United States Patent 3,140,417 ELECTREC LAMP STEM WITH STRAIN RELIEVING SLEEVE Alfred Tietze, Berlin-Neukolln, Germany, assignor to Patent-Treuhand-Gesellschaft fiir elelrtrische 'Gliihlampen rn.b.H.

Filed Dec. 18, 1961, Ser. No. 159,923 Claims priority, application Germany Jan. 16, 1961 9 Claims. (Cl. 313-256) The invention refers to electrode seals or stems for electric lamps and particularly suitable for high pressure discharge lamps.

The electrodes of such lamps have inleads hermetrically sealed into the discharge envelope. However, according to the general practice heretofore, the seal extends only over a relatively short portion of the rod-shaped electrode current inlead and is often subject to high stresses due to the weight and length of the electrode. As a result, cracks may occur in the sealing material and the electrode seal becomes permeable to air.

In order to reduce these high stresses, it is well known to provide additional support to the inlead at a point closer to the arc by shaping or constricting the envelope neck over a certain length so that it surrounds or encircles snugly the inlead close to the point where the electrode is attached to it. A hermetic seal is not made at this point and sufficient play or clearance is maintained, as required by the coefficient of expansion of the inlead rod, to avoid binding and fracture of the neck. Sometimes a foil is wrapped around the inlead rod to assure that no hermetic seal is made at the constriction.

The above arrangement suffers from the great disadvantage that a dead space is brought about, that is a space separated from the discharge vessel but not hermetically sealed off. This space occurs between the support point or constriction, and the hermetically sealed end of the lead-in and it cannot be evacuated or at best it can only by evacuated very slowly. As a result, a continuous penetration of residual air from the dead space into the discharge space takes place or in the case of a finished lamp, gas from the discharge space is lost by leaking into the dead space.

A support of the foregoing kind cannot be made impermeable to air, because the inlead rod must not be tightly surrounded by or sealed to the material of the vessel. Otherwise, the different coeificients of expansion of the current inlead and of the material of the vessel will result in fracture of the vessel or envelope neck. A further disadvantage is that the stability of the support is reduced by its relatively small cross section.

The aforesaid drawbacks of such support arrangements for the inleads are overcome by the construction according to the invention. The electrode seal or stem according to the invention for high pressure lamps, particularly for rare-gas high pressure discharge lamps, is characterized in that at least one cylindrically shaped sleeve with a coeflicient of expansion similar to that of the envelope material is placed in the envelope neck between the electrode and the hermetic seal of the lead-in to the current conductor. The sleeve surrounds the rod-shaped current inlead of the electrode and has its shell or outer surface sealed or fused to the envelope neck. It is so shaped or apertured that the discharge space and the space around the lead-in of the current conductor are interconnected within the evacuated lamp. The lead-in of the current conductor placed behind the sleeve can be made as a rod seal or as foil seal and a base shell or terminal may be attached or connected thereto on the outside of the lamp.

The external cylindrical surface of the sleeve or sleeves is provided with longitudinally extending grooves or slits. These constitute passageways between the lamp proper 3,140,417. Patented July 7, 1964 and the space behind the sleeve, and allow a more rapid compensation or equalization of pressure between the two volumes. Thus, evacuation of the space behind the sleeve occurs rapidly during the exhausting process of the discharge vessel. During filling of the lamp, equilibrium of gas or vapor pressure in the discharge vessel is achieved within a short time. The interconnection of the discharge space and the space behind the sleeve can also be achieved by providing the sleeve with axial holes or borings in lieu of or in addition to the slits or grooves.

For reasons of stability and heat conduction the number or cross section of the slits or borings in the sleeve cannot be increased arbitrarily. Therefore, it is generally desirable to provide not more than 8 borings or slits; the sleeve is, preferably, provided with 4 slits or borings. The slits should not be deeper than half the sleeve wall thickness or radius and the width of the slits should preferably not exceed th of the sleeve diameter.

The sleeve should provide support to the rod-like current inlead at a minimum of two points spaced apart more than 4 times the diameter and preferably in the range of 8 to 12 times the diameter of the rod-like inlead. Where a single sleeve is used, its length should be in the range of 8 to 12 times the diameter of the inlead. However, instead of one long sleeve, two or more shorter sleeves can be used according to the invention in order to reduce the evacuation resistance. In such case the distance between the extremities of the sleeves should be more than 4 times, preferably 8 to 12 times the diameter of the electrode-rod.

The special construction of a sleeve according to the invention, provided primarily for reduction of strain, also makes it possible to provide the exhaust tube at the end of the lamp behind the sleeve instead of on the central body of the lamp envelope, and to exhaust and fill the lamp through stem and sleeve.

In the drawings wherein like reference characters denote corresponding parts or elements throughout the several views:

FIGS. 1a to 1d show lamp stems with rod type electrode seals embodying the invention.

FIGS. 2a and 2b show lamp stems with foil type seals embodying the invention.

FIGS. 3a to 32 illustrate various types of sleeves which may be used in the seals of the preceding figures.

FIG. 1a is a longitudinal section through a rod type electrode seal prior to assembly into a lamp stem. The current inlead 1 is a rod of tungsten. Its inner end proximate to the arc carries an electrode 2, and its outer end remote from the arc is provided in well-known manner with a seal 3. The seal comprises a customary glasscoat portion 4 hermetically sealed to rod 1 and having the same coefficient of expansion as tungsten, a portion 5 of transition glasses, and a tubular shell 6 of quartz glass united to the transistion glass portion 5 at its inner end and having a skirt 7 at its outer end which approaches and encircles the outer end of inlead 1.

Before the electrode 2 is attached to the current inlead 1, a sleeve 8 of quartz glass provided with a central boring or hole 9 and with longitudinally extending slits 10 is slipped over the current inlead 1. The hole through the sleeve is large enough to accommodate the inlead rod preferably snugly but without binding at any temperatures to which it may be subjected. An envelope 11 of quartz glass is then placed over the electrode seal according to the assembly illustrated in FIG. 1b, which shows a finished rod type stem according to the invention. The neck portion of envelope 11 is sealed at 12 to the quartz glass shell 6. Thereafter envelope 11 is exhausted and heated up in the region 13 where it overlaps sleeve 8 till it softens and collapses and seals together with the outer surface of the sleeve.

FIG. 10 shows a'variant in stem electrode assembly. A tube 14 of quartz is placed over electrode seal 3 and joined or fusion-sealed thereto at 12, and also collapsed in the region 13 to seal to the outer surface of sleeve 8'. Envelope 11 is then placed over tube 12 so as to overlap it in the region 15 and then heated to effect a fusion-seal at 15.

FIG. 1d shows a rod type lamp stem assembly utilizing a simpler form of seal 3a suitable for medium pressure lamps. The glass coat portion 4a of the seal is hermetically sealed to inlead rod 1 near its outer extremity. Then progressively inwardstherefrom occurportion 5a of transition glasses, portion 6a of quartz, and seal junction 12a to envelope 11. The envelope, as before, is collapsed and fused to sleeve 8 in the region 13.

FIG. 2a shows a stem assembly utilizing a foil type seal. The outer end of inlead 1 is welded to a thin molybdenum foil 16. A short piece of rod 17 is welded to the outer end of the foil to provide an external terminal. Then the neck-like extension of envelope 11 is collapsed and pinched'over the foil in the region 18 to effect a hermetic seal which depends upon the use of a very thin cross-section in the foil rather than a match between coefiicients of expansion. The inlead rod 1 is supported by sleeve 8 to which the envelope is fused in the region 13.

FIG. 2b shows a stem assembly utilizing variants in foil seal construction and in the sleeve. The molybdenum foil is pinched-sealed within a short length of quartz tubing 19 provided with a skirt 20 at its outer end. Skirt 20 approaches and encircles the outer end of terminal rod 17 to give it additional support. Instead of a single relatively long sleeve, two short sleeves 8a and 8b spaced apart with a gap in between are utilized to provide additional support to inlead rod 1. The envelope is collapsed and fused to the sleeves in the regions 13a and 13b.

FIGS. 3a and 3b show longitudinal and end views of sleeve 8 provided with a central boring or hole 9 and lateral longitudinally extending slits 10.

FIGS. 30 to 30 are end views of variants in the construction of sleeve 8. In FIG. 3c, keystone-shaped slots 21 are provided extending longitudinally in the sides of the sleeve. In FIG. 3d, instead of lateral slits or slots, a plurality of longitudinally extending holes or passageways 22 are provided in the body of the sleeve. In FIG. 3e, both longitudinally extending slots in the sides and holes 22 in the body of the sleeve are utilized.

By way of example, the dimensions in two different lamp stems illustrative of the invention are as follows. In one example wherein the diameter of current inlead 1 is 2.4 mm., the sleeve diameter is 8 mm. and the sleeve length is 24 mm.; slits 10 are about 1.3 mm. deep and 0.4 mm. wide, and the diameter of holes 22 is about 0.8 mm. In another example wherein the diameter of current inlead 1 is 8 mm., the sleeve diameter is 20 mm. and the sleeve length is 80 mm.; the slits 10 are about 3 mm. deep and 1 mm. wide, and the diameter of holes 22 is about 2 mm.

The method of constructing lamp stems in accordance with the invention achieves greater ease of manufacture and results in a construction in which there is less variation between units and which is stronger and more resistant to breakage.

The preferred embodiments of the invention which have been illustrated and specifically described are intended by way of example only, and the scope of the invention is to be determined by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric lamp stern comprising a tubular vitreous neck portion and rod-like current inlead extending longitudinally therethrough for supporting an electrode forward of its inner end, a hermetic seal at the outer end of said inlead joined to the outer end of said neck portion,

and at least one generally cylindrical sleeve having a coefiicient of expansion substantially equal to that of said neck portion located within said neck portion and having an axial hole therethrough through which said inlead extends with a snug fit but without binding, the outer surface of said sleeve being fused to the inner surface of said neck portion, said sleeve having longitudinally extending passageways therethrough interconnecting the space between the outer end of said sleeve and said hermetic seal with the space forward of the inner end of said sleeve.

2. An electric lamp stern as defined in claim 1 wherein the passageways through said sleeve are formed by longitudinally extending grooves in its outer surface.

3. An electric lamp stem as defined in claim 1 wherein the passageways through said sleeve are formed by longitudinally extending holes.

4. An electric lamp stem as defined in claim 1 wherein said sleeve, which provides support to said rod-like inlead, has a length at least 4 times the diameter of said inlead.

5. An electric lamp stem as defined in claim 1 wherein said sleeve, which provides support to said rod-like inlead, has a length in the range of 8 to 12 times the diameter of said inlead.

6. An electric lamp stem as defined in claim 1 having more than one sleeve for support to said rod-like inlead, the distance between neighbored sleeves being at least 4 times the diameter of said inlead.

7. An electric lamp stern as defined in claim 1 having I more than one sleeve for support to said rod-like inlead,

7 glass-coat portion to the outer end of said neck portion,

and at least one generally cylindrical sleeve having a coefiicient of expansion substantially equal to that of said neck portion located within said neck portion and having an axial hole therethrough through which said inlead extends with a snug fit but without binding, the outer surface of said sleeve being fused to the inner surface of said neck portion, said sleeve having longitudinally extending passageways therethrough interconnecting the space between the outer end of said sleeve and said hermetic seal with the space forward of the inner end of said sleeve.

9. An electric lamp stem comprising a tubular quartz neck portion and a rod-like current inlead extending longitudinally therethrough for supporting an electrode forward of its inner end, a hermetic seal at the outer end of said inlead comprising a thin foil conductor sealed through a quartz portion, said foil conductor being joined to the outer end of said inlead and said quartz portion besealed to the outer end of said neck portion, and at least one generally cylindrical quartz sleeve located within said neck portion and having an axial hole therethrough through which said inlead extends with a snug fit but without binding, the outer surface of said sleeve being fused to the inner surface of said neck portion, said sleeve having longitudinally extending passageways therethrough interconnecting the space between the outer end of said sleeve and said hermetic seal with the space forward of the inner end of said sleeve.

References Cited in the file of this patent UNITED STATES PATENTS 2,282,325 Epstein May 12, 1942 2,288,861 Watrous July 7, 1942 2,670,399 Freeman et al Feb. 23, 1954 3,080,497 Noel et al Mar. 5, 1963 

1. AN ELECTRIC LAMP STEM COMPRISING A TUBULAR VITREOUS NECK PORTION AND ROD-LIKE CURRENT INLEAD EXTENDING LONGITUDINALLY THERETHROUGH FOR SUPPORTING AN ELECTRODE FORWARD OF ITS INNER END, A HERMETIC SEAL AT THE OUTER END OF SAID INLEAD JOINED TO THE OUTER END OF SAID NECK PORTION, AND AT LEAST ONE GENERALLY CYLINDRICAL SLEEVE HAVING A COEFFICIENT OF EXPANSION SUBSTANTIALLY EQUAL TO THAT OF SAID NECK PORTION LOCATED WITHIN SAID NECK PORTION AND HAVING AN AXIAL HOLE THERETHROUGH THROUGH WHICH SAID INLEAD EXTENDS WITH A SNUG FIT BUT WITHOUT BINDING, THE OUTER SURFACE OF SAID SLEEVE BEING FUSED TO THE INNER SURFACE OF SAID NECK PORTION, SAID SLEEVE HAVING LONGITUDINALLY EXTENDING PASSAGEWAYS THERETHROUGH INTERCONNECTING THE SPACE BETWEEN THE OUTER END OF SAID SLEEVE AND SAID HERMETIC SEAL WITH THE SPACE FORWARD OF THE INNER END OF SAID SLEEVE. 